That child is recovering, and no other members of the camping party have reported any related symptoms.

Photos:Plague: a scourge of biblical proportions

Photos:Plague: a scourge of biblical proportions

This is what causes the plague. Yersinia pestis bacteria, colored in yellow, are seen on the spines inside a flea's digestive system.

Hide Caption

1 of 7

Photos:Plague: a scourge of biblical proportions

The bacterium that is responsible for the plague can sometimes infect the blood, causing the hands, feet, nose and lips to become gangrenous and black. This form of the disease is almost always fatal if not treated with antibiotics.

Hide Caption

2 of 7

Photos:Plague: a scourge of biblical proportions

A map shows reported cases of human plague in the United States from 1970 to 2012. Nearly all cases occur in the western U.S., for reasons that are not entirely understood. Plague first came to the U.S. in 1900 via rats on steamships from Asia.

Hide Caption

3 of 7

Photos:Plague: a scourge of biblical proportions

Rats are one of the many rodent species that carry the plague. The disease is typically spread to people through a bite from a rodent flea. Although recent research may exonerate rats as primarily responsible for the Black Death, and instead put the blame on gerbils, rats probably played a role in that and other plague epidemics.

Hide Caption

4 of 7

Photos:Plague: a scourge of biblical proportions

The plague doctor is in. The hat, goggles, gown and beak-like mask identified a person as a plague doctor in the Middle Ages. The uniform was used for protection; the beak contained herbs and perfumes intended to cover the stench associated with plague disease.

Hide Caption

5 of 7

Photos:Plague: a scourge of biblical proportions

A patient with plague symptoms, foreground, awaits test results with his mother at New Delhi's Disease Hospital in 1994. Pneumonic plague, which infects the lungs, is the most serious form of the disease and the only way it can spread directly between people. A plague outbreak in India in 1994 was among the most serious in the world in recent decades.

Hide Caption

6 of 7

Photos:Plague: a scourge of biblical proportions

Taylor Gaes died of the plague this spring, a day before he would have turned 16. Officials think he was infected from a flea bite on his family's ranch in Larimer County, Colorado. The high school sophomore began having flu-like symptoms after he pitched in a baseball game. Although plague remains rare, it is often mistaken for the flu because it causes fever and chills.

Hide Caption

7 of 7

Still, authorities are monitoring them as well as warning others to be on guard against the flea-transmitted disease. These extra steps include putting up caution signs at Crane Flat and other campgrounds and urging people to take precautions such as:

• Not feeding squirrels, chipmunks or other rodents or touching sick or dead ones

Read More

• Avoiding hiking or camping near rodent burrows

• Putting on long pants tucked into socks or boots with the hope they'll provide a barrier to fleas

The Centers for Disease Control and Prevention reports that the United States has about seven annual cases, over 80% of which have been in the bubonic form.

There have been three cases reported so far in 2015, which is in line with those numbers. The other two happened in Colorado and both resulted in deaths, one being a teenager in Larimer County and the other an adult in Pueblo County, as announced Wednesday by the local health department.

The Yosemite case is California's first instance of human plague since 2006, according to state health officer Dr. Karen Smith, when there were three cases in Mono, Los Angeles and Kern counties. There have been 42 such cases in the state since 1970, of which nine proved fatal.

"Although this is a rare disease, people should protect themselves from infection by avoiding any contact with wild rodents," Smith said.